The present invention relates to the recovery of solid rubber-modified polymer particles from high rubber latexes. More particularly, the present invention relates to a process for promoting large particle formation and syneresis in acrylonitrile-butadiene-styrene resin (ABS) production and to the product thereby produced.
Rubber-modified polymers are conventionally made by preparing a rubber latex by emulsion polymerization and then polymerizing matrix monomers in the presence of the rubber latex. The latex solids are then recovered from the latex for subsequent compounding and use. One method for recovering latex solids is taught in U.S. Pat. No. 4,299,952, Nov. 10, 1981 to Pingel, et al. The Pingel, et al. patent teaches a shear coagulation process wherein a latex is shear coagulated to form a paste, which is then subjected to finishing steps of heating and shearing to form a crumb which is mechanically dewatered and ground to a desired particle size.
It has been found, however, that some latex solids are unfinishable due to their inability to synerese and form hard distinct particles that can be mechanically dewatered. ABS solids of high rubber content, i.e., of greater than about 50% rubber, give rise to such finishing problems. The process of the present invention provides a method by which previously unfinishable latexes can be finished and consequently also a method by which a wide range of latexes including ABS resins of high rubber content can be made by an emulsion polymerization--shear coagulation process. Surprisingly, not only does the present method facilitate finishing of high rubber latexes, the product of the method has improved gloss, elongation and impact strength. These and still other advantages of the present invention will be apparent from the following description taken in conjunction with the drawings and claims. All percentages and parts herein are by weight unless otherwise indicated.